Torque motor operated spool valves are well-known in the art as evidenced by the number of patents issued by the United States Patent and Trademark Office related to such valves. A typical torque motor driven spool valve includes a movable member disposed within a bore having an inlet port and an outlet port to provide communication between a supply passage and a load passage in a controlled fashion in response to an application of an electrical signal to an electrically driven torque motor. This electrically driven torque motor is operatively interconnected with the valve member. Typical of United States patents issued on inventions relating to spool valves is U.S. Pat. No. 3,040,768, entitled "OSCILLATING VALVE".
As disclosed in U.S. Pat. No. 3,040,768, an electric motor is secured to the valve housing and drives a shaft that includes an eccentric pin fitted into an annular groove. This mechanism and the operation thereof imparts an oscillatory motion to a ported sleeve to prevent sticking or binding of the spool. To prevent this sticking or binding the eccentric pin is continuously rotated to impart a high frequency, low amplitude "dither" to the ported sleeve. Metering or control of flow through the valve is achieved by independently actuated drive solenoids operatively engaging the ported sleeve.